Natasha Wills, of London Ambulance Service said: "We were called at 8.20am to reports of an incident at Parsons Green underground station.

"We have sent multiple resources to the scene including single responders in cars, ambulance crews, incident response officers and our hazardous area response team, with the first of our medics arriving in under five minutes.

"Our initial priority is to assess the level and nature of injuries. More information will follow when we have it."

BBC correspondent Riz Lateef, who was at the station travelling to work, said there was "panic as people rushed from the train, hearing what appeared to be an explosion.

"People were left with cuts and grazes from trying to flee the scene. There was lots of panic."

One passenger, named only as Lucas, told BBC 5 live: "I heard a really loud explosion - when I looked back there appeared to be a bag but I don't know if it's associated with it.

"I saw people with minor injuries, burnings to the face, arms, legs, multiple casualties in that way.

"People were helping each other."

Transport for London said Tube services were suspended between Edgware Road and Wimbledon.

In a statement, Scotland Yard said: "Police were called at approximately 8.20am to Parsons Green Underground Station following reports of an incident on a Tube train.

"Officers from the Metropolitan Police Service and British Transport Police are in attendance along with the London Fire Brigade and London Ambulance Service.

"We would advise people to avoid the area."

Another witness, Sham, said he saw a man with blood all over his face.

"There were loads of people crying and shaking," he told 5 live.

"There were a lot of people limping and covered in blood.

"One guy I saw, his face was covered in blood - I've never seen anything like it."

London Fire Brigade said six fire engines, a fire rescue unit and around 50 firefighters and specialist officers were sent to the scene.

Commuter Robyn Frost was arriving at the station when she saw people trying to escape.

She told the BBC: "I walked into the station, there was blood on the floor and people running down the stairs screaming 'get out'.

"People were coming out of the station covered in blood."

She added: "People have been stretchered into ambulances now."

BBC News presenter Sophie Raworth, who was at the scene, said she saw a woman on a stretcher with burns to her face and legs.

"I spoke to a woman, Laura Bishop, who said she was standing there and all of a sudden heard a bang - and saw a wall of flames, flames in the carriage," she said.

"She saw people who had burns on their hair, burns on their head and the doors opened immediately."